The handy RS-232 model includes both current loop and ground potential testings. 102 dual-state LEDs show positive voltage, negative voltage, or no voltage at all on each side of all 25 leads on a DB25 interface connection, or 9 leads on a DB9 interface connection. And the box comes complete with two DB9 DB25 adapters, so you're sure to be able to use it with your system. Additional tests performed by the box include potential test and 4-level bi-directional current-loop test. The box features six single one-to-one jumpers and two four-way jumpers.